Device for temperature controlled housing of a planar optical component

ABSTRACT

The present invention relates to an improved device for housing a planar optical component for use in chemical sensing for example which permits fine temperature control and disposal of heat.

Priority is claimed under 35 USC §371 of International ApplicationNumber PCT/GB00/03536, filed Sep. 22, 2000 which claims priority underArticle 4 of the Paris Convention to United Kingdom Patent ApplicationNumber 9922601.1, filed 24 Sep. 1999.

The present invention relates to an improved device for housing a planaroptical component for use in chemical sensing for example.

New chemical sensor technologies using optical techniques (in particularinterferometric techniques) are providing new high performance devices.Whilst these devices are relatively simple in terms of components, thetolerances required in the assembly-procedure can be extremely onerous.Of these, end illuminated interferometric devices are perhaps the mostdemanding. In such cases, sub-micron misalignment between theelectromagnetic radiation source (typically a collimated, focussedlaser) and the sensor substrate itself may be sufficient to prevent itscorrect operation.

There are several situations which may lead to distorted output from aconventional device. Thus, the light beam may pass over the top of theplanar optical component and distort the output received by-thedetector. Similarly, where the device comprises a planar sensingwaveguide and a planar reference waveguide, if the light misses awaveguide or fails to illuminate both equally, the output may be lost ordistorted. Thus, if any of the components (eg light source, lenses,polarisers, sensors etc) are misaligned by as little as 2×10⁻⁷ metres(200 nm) the performance of the device will be adversely effected. Theprovision of a device which ensures that waveguides are illuminatedequally without admitting stray light represents a significant technicalchallenge.

More generally, there is a need for sensor assemblies of simplerconstruction and improved reliability. The range and applicability ofchemical sensors could be greatly enhanced if it were possible toachieve lower manufacturing costs and greater robustness. An importantconsideration in developing suitable devices is temperature management.This imposes various design constraints related to the thermal mass ofareas requiring insulation and the disposal of unwanted heat into theenvironment.

The present invention seeks to provide an improved device for housing aplanar optical component such as a chemical sensor which is-capable ofultra high precision temperature control. The device is advantageouslyrobust and gives enhanced signal to noise ratios (sensitivity).Moreover, the invention seeks to provide an optical (interferometric)chemical sensor device which is simple to machine and assemble and faulttolerant in terms of construction errors and which may be used to obtainreliable information relating to the changes occurring within thedevice.

Thus viewed from one aspect the present invention provides a devicecomprising:

an optical assembly adapted to mount a planar optical component (eg asensor) so as to define a longitudinal path through the device in whichthe planar optical component is effectively exposed in free space andincluding guiding means for correlating along said longitudinal path theposition of said planar optical component and of a source ofelectromagnetic radiation, whereby to expose said planar opticalcomponent to said electromagnetic radiation along said longitudinal pathwhilst substantially eliminating stray electromagnetic radiation,

wherein the optical assembly comprises a cavity which permits access toa face of the planar optical component or a face of a base with whichthe planar optical component is in intimate thermal contact whereby toenable an inner temperature controller to be positioned in thermalcontact with the planar optical component for controlling thetemperature of the planar optical component.

The inner temperature controller is capable of permitting finetemperature control of the planar optical component (eg sensor) and maybe a heat pump or thermo-electric controller capable of providing orremoving heat as desired. In a preferred embodiment, the innertemperature controller is an inner Peltier assembly capable of addingheat to or dissipating heat from the planar optical component. The innerPeltier assembly may comprise an inner Peltier mounted on an innerPeltier mount. The inner Peltier mount conveniently provides thermalmass. Preferably, the Peltier mount has a concave underside to optimisethermal contact with the planar optical component (or its base). Theinner Peltier and inner Peltier mount may be provided with suitableinsulation as desired.

Preferably the planar optical component is a sensor. In a preferredembodiment, the sensor is mounted on a sensor base and is in intimatethermal contact therewith. The base is typically made of stainless steelwhich advantageously provides thermal mass. Preferably the opticalassembly is thermally insulating to permit the sensor, sensor base andPeltier mount to be in intimate thermal contact with the inner Peltierand thermally isolated from other components of the device.

Preferably the device is provided with a Peltier exhaust assembly whichpermits thermal transfer from the exhaust side of the inner Peltier tothe environment.

Preferably the Peltier exhaust assembly comprises an exhaust platepositioned to allow thermal exchange with the environment. The exhaustplate is conveniently located at or near to an end of the device remotefrom the optical assembly. Preferably the Peltier exhaust assemblycomprises means for thermally contacting the inner Peltier assembly withthe exhaust plate. A thermally conducting strip may be used for thispurpose (eg of copper). Preferably, the Peltier exhaust assemblycomprises an exhaust guide (eg in the form of a ring) which is capableof fitting over the insulating collar of the laser module. The exhaustguide defines a slot into which the exhaust strip may be inserted.

In a preferred embodiment, the optical assembly and inner temperaturecontroller are contained within a conducting sleeve. The conductingsleeve fulfils thermal management of the temperature sensitivecomponents of the device eg provides a highly stable temperatureenvironment for the inner temperature controller, provides precisiontemperature control for peripheral components such as the laser diode,provides a thermally stable environment for temperature controlelectronics and controls the temperature of incoming gases or liquidsthrough the inlet and outlet ports. All these functions contribute tothe temperature of the planar optical component being contained withindesirable limits (typically the target control span is 20 micro Kelvin).

In a preferred embodiment, the conducting sleeve comprises a heat shroudwhich is typically made of copper. The heat shroud is preferablyprovided with an opening which is suitably disposed to coincide with thecavity in the optical assembly. This advantageously allows the innerPeltier assembly to be inserted in the optical assembly, after theoptical assembly has been inserted in the conducting sleeve (eg heatshroud).

Preferably, the heat shroud comprises an integral laser module holderfor inserting a laser module. Preferably the laser module holder isprovided with an outwardly disposed insulating collar. Preferably theelectronics are housed within the heat shroud.

Preferably the device comprises an outer temperature controller-whichpermits-coarse temperature control of for example the conducting sleeve,laser module, laser module holder, the exterior parts of the opticalassembly and the electronics. The outer temperature controller isthermally independent of the inner temperature controller. The outertemperature controller conveniently takes the form of an outer Peltierassembly. Preferably, the outer Peltier assembly is provided externallyof the restraining sleeve which is provided with an aperture to enableexposure of an effective area of the conducting sleeve to achievethermal contact with the outer Peltier assembly.

Preferably, the device is provided with a means for urging the Peltierexhaust assembly onto the inner Peltier assembly. For example, arestraining sleeve is added outwardly of the heat shroud to force thePeltier exhaust assembly onto the inner Peltier assembly at one end andthe exhaust plate at the other.

A preferred device of the invention is based on the principle of “aRussian doll” which has the advantage of being able to be constructedfrom a plurality of discrete assemblies. The assemblies of the devicemay be constructed as a plurality of shells which allow advantageouslystraightforward, sequential construction of the overall device.

Thus a preferred embodiment of the device of the invention is capable ofsequential construction from a plurality of discrete assemblies, saidassemblies being: an optical assembly contained within a conductingsleeve; an inner Peltier assembly comprising an inner Peltier; and aPeltier exhaust assembly,

wherein: the inner Peltier assembly is housed within the cavity of theoptical assembly so-as to achieve intimate thermal contact with theplanar optical component and the Peltier exhaust assembly permitsthermal transfer from the exhaust side of the inner Peltier to theenvironment and is thermally isolated from the inner Peltier assemblyand conducting sleeve.

Particularly preferably, this embodiment further comprises a discreteassembly being an outer Peltier assembly in thermal contact with theconducting sleeve.

Viewed from a further aspect the present invention provides a kitcapable of being assembled into a device as hereinbefore defined, saidkit comprising:

an optical assembly, an inner Peltier assembly, a conducting sleeve, aPeltier exhaust assembly and an outer Peltier assembly, wherein:

the optical assembly is capable of being inserted in the conductingsleeve;

the inner Peltier assembly is capable of being housed within the cavityof the optical assembly so as to achieve intimate thermal contact withthe planar optical component; the Peltier exhaust assembly is capable ofbeing-positioned in thermal isolation from the conducting sleeve so asto permit thermal transfer from the exhaust side of the inner Peltier tothe environment; and the outer Peltier assembly is capable of beingpositioned so as to achieve thermal contact with the conducting sleeve.

Viewed from a yet further aspect the present invention provides the useof a device or kit as hereinbefore described as a gas or liquid sensor.

Viewed from a still yet further aspect the present invention provides aprocess for constructing a device as hereinbefore defined comprising thesteps of:

inserting an optical assembly in a conducting sleeve (eg copper heatshroud) comprising an integral laser module housing;

inserting a laser module into the laser module housing;

housing an inner Peltier assembly in the cavity of the optical assemblyso as to achieve thermal contact with the planar optical component;

positioning a Peltier exhaust assembly in thermal isolation from theconducting sleeve so as to permit thermal transfer from the exhaust sideof the inner Peltier to the environment.

Where appropriate, the process of the invention may comprise theadditional steps of:

constructing an outer restraining sleeve;

constructing an outer casing; and

positioning an outer Peltier assembly on the outer casing or restrainingassembly whereby to achieve thermal contact with the conducting sleeve.

In order to impart optimum thermal performance to the device, thematerials of the various component parts are judiciously chosen. Wherenecessary, component parts may be required to have good insulating andmechanical properties, thermal drive (good thermal conductor), thermalexhaust (good thermal conductor), high performance insulating propertiesand mechanical properties, high performance insulating properties, etc.Materials for these purposes will be, familiar to those skilled in theart.

The exclusion of stray radiation in accordance with the optical assemblyof the device of the invention enables the number of components to beminimised and enables straightforward analysis of the signals generatedby the planar optical component (such as the centre of gravity of aseries of interferometric fringes for example). This is achieved byensuring that electromagnetic radiation excites substantially only theplanar optical component. The optical assembly of the device of theinvention is suitable for the fault tolerant construction of planaroptical sensors and ensures optimal performance from the planar opticalcomponent. Tolerances are typically reduced by approximately 1000 foldenabling cheap mass production methods such as compression moulding andinjection moulding to be employed.

In a preferred embodiment, the optical assembly of the device accordingto the invention comprises a planar optical component having a pluralityof waveguides. Typically the planar optical component comprises asensing waveguide and a reference waveguide. Preferably the planaroptical component is any of those described in WO-A-98/22807 (IMCO(1097) Ltd et al).

Preferably the optical assembly is provided with one or more seats uponwhich the planar optical component may be seated.

The optical assembly may comprise a holder for mounting the planaroptical component and a housing adapted to receive internally saidholder so as to define a longitudinal path through the device in whichthe planar optical component is effectively exposed in free space.Preferably the holder comprises a basal recess in which the planaroptical component may be mounted. To ensure that the edge of the planaroptical component which is to be excited by the electromagneticradiation is suitably exposed in the longitudinal path, one or morelongitudinal cavities may be provided in the base of the holder suchthat when the planar optical component is positioned adjacent anaperture in the housing, the majority of the leading and trailing edgesof the planar optical component may be exposed in free space. In aparticularly preferred embodiment of the invention, the holder isremovably received in the housing. The provision of a holder of thistype advantageously enables the planar optical component (eg sensor) tobe replaced without discarding or rebuilding the supporting components.Where appropriate, the optical assembly of the device of the inventionmay provide a means for providing a constant force between the holderand the housing.

Preferably the optical assembly of the device of the invention includesa guiding means in the form of a spacer incorporated in the planaroptical component or in the main body of the optical assembly. In thefirst instance, the spacer may be incorporated in the planar opticalcomponent conventionally during manufacture. In the second instance, thespacer takes the form of (or is located on) a seat in the opticalassembly upon which the planar optical component is located in use. Thislatter embodiment has the advantages that the sensing layer of theplanar optical component is more efficiently exposed to the testmaterial, that the manufacture of the planar optical component issimplified and that the disturbance of the planar optical component (asa result of bringing it into contact with the seat or with the modifiedseat upon which the spacer is located) is minimised. The material fromwhich the spacer is made is judiciously chosen in terms of refractiveindex and physical properties. The spacer is advantageously permeable tothe sample under analysis.

In a preferred embodiment, the optical assembly of the device of theinvention comprises a first aperture at a first end of a longitudinalpath for admitting electromagnetic radiation and a second aperture at asecond end of said longitudinal path for transmitting electromagneticradiation. Provided the spacer is of a known predetermined thicknessrelative to the known distance between the first aperture and thesurface upon which the planar optical component is seated within theoptical assembly, electromagnetic radiation may be effectively guidedonto the waveguides.

In a particularly preferred embodiment, the planar optical component andincorporated spacer may be located on a silicon baseplate. The siliconbaseplate which is typically optically flat may be conveniently providedwith a hole over which the planar optical component is located.Conveniently, the spacer may seal the hole in the baseplate provided thespacer is sufficiently (eg optically) flat.

In an especially preferred embodiment, the silicon baseplate is providedwith a channel (eg a V-shaped channel) capable of receiving an opticalfibre wherein the depth of the channel predetermines the position andheight that electromagnetic radiation is emitted relative to the surfaceof the silicon baseplate. Since the position of the waveguides above thesurface of the silicon baseplate is determined by the height of theincorporated spacer, the position of the electromagnetic radiation andthe waveguides may be correlated. Stray light is simply emitted into thesilicon.

In an alternative especially preferred embodiment, the silicon baseplateforms part of an integrated electro-optic device in which a laser sourceis integrated into the silicon baseplate. The guiding means is providedby an incorporated spacer located on the silicon baseplate or the planaroptical component as hereinbefore described.

In either of the especially preferred embodiments, the output may bemonitored by a discrete detector or an imaging fibre or fibre array maybe used to collect the output image. Alternatively, a photodetectorcould be integrated into the silicon structure. Using fibres in and outis very useful in safety critical applications (ie there is noelectricity).

Preferably, the optical assembly of the device of the inventioncomprises means (eg a flat surface, one or more seats or seals) forproviding a gas or liquid seal to the surface of the planar opticalcomponent to allow transport of an analyte to and from the planaroptical component (eg sensor) and measurement of the optical behaviourof the component in the presence of the analyte. The provision of a sealto the surface of the planar optical component (eg sensor) reduces thedead volume to a minimum (this is important in providing optimalperformance with chemical sensors). The provision of a seal to thesurface of the planar optical component (eg sensor) also enables liquidsamples to be used in addition to gas samples. This is not conceivablewith a conventional freestanding arrangement as wetting of the end faceswould lead to optical misalignment.

Preferably, the optical assembly of the device of the invention iscapable of mounting an electromagnetic radiation source such as a laser.Preferably, the optical assembly is capable of mounting anelectromagnetic radiation detection device (eg photodiode array).Preferably, the optical assembly of the device of the inventioncomprises means for the provision of removable or non-removablecomponents between the planar optical component (eg chemical sensor) anda source of electromagnetic radiation and/or between the planar opticalcomponent and a radiation detection device. Such components may beconventional lenses, polarisers, electromagnetic radiation windows,spacers, window/spacer retainers, etc mounted in a conventional manner.

In all cases, the body of the optical assembly is preferably opaque tominimise stray electromagnetic radiation. Thus the planar opticalcomponent may be advantageously mounted on a base which does nottransmit electromagnetic radiation, thereby preventing strayelectromagnetic radiation passing thereunder. Preferably, the seat orseal of the optical assembly also may not transmit electromagneticradiation in the longitudinal direction whereby to further prevent strayelectromagnetic radiation passing over the sensor surface and reachingthe detector. Preferably, the seat or seal has an inlet, a channel andan outlet providing a means through which analyte (eg gases or liquids)may pass. In this way, analyte is able to pass into and out of theabsorbent layers of a planar optical component (eg chemical sensor)leading to measurable changes in the output electromagnetic radiation.Preferably, the extremes (edges) of the sensor are sealed from theenvironment to prevent extraneous effects from gases, vapours or liquidsfrom external sources not related to the sample under analysis.

In a preferred embodiment, where the device of the invention is to beused on test materials, it is preferred that the thermal mass of theincoming material is minimised by ensuring the sample volume and theinlet volume are minimised. This may be achieved by low dead volumewithin the sensor “cavity” and narrow bore inlets. In addition, thethermal mass of the inlet system needs to be high to prevent thermalfluctuation over time. Stainless steel pipework is preferred.Preferably, the inlet pipe is in thermal contact with the copper shroudeg the pipework is run along the shroud. Appropriate thermal lagging ofthe pipework may be required in order to prevent too high a thermal lossfrom the complete outer system.

The invention will now be described in preferred embodiments in anon-limitative sense with reference to the accompanying Figures inwhich:

FIG. 1 illustrates a bottom view of a holder of an optical assembly inaccordance with an embodiment of the invention;

FIG. 2 illustrates an end elevation of a holder positioned within ahousing of an optical assembly in accordance with an embodiment theinvention;

FIG. 3 illustrates a cross-sectional disassembled view of an opticalassembly of an embodiment of the invention;

FIG. 4 illustrates an exploded view of a cross-section of an opticalassembly of a disassembled embodiment of the invention;

FIG. 5 illustrates a top view of a housing and a partial side view of aholder within the housing of an optical assembly in accordance with anembodiment of the invention;

FIG. 6 illustrates an optical assembly of an embodiment of theinvention;

FIG. 7 illustrates an optical assembly of a further embodiment of theinvention;

FIG. 8 illustrates an optical assembly of a further embodiment of theinvention;

FIG. 9 illustrates an optical assembly of a further embodiment of theinvention; and

FIGS. 10 to 18 illustrate the components and stages of construction ofan embodiment of the device of the invention.

FIG. 1 illustrates a holder 2 in which a planar optical component(sensor) 3 is mounted in a basal recess 1. Longitudinal cavities 4 a and4 b are provided along a longitudinal path to allow the sensor to bepositioned adjacent an aperture in a housing (of the type shown in FIGS.2 and 5) so as to ensure that the majority of the leading and trailingedges of the sensor are exposed in free space.

FIG. 2 shows an end elevation of the optical assembly 21 of a device ofthe invention with a holder 22 positioned within a housing 27 in such amanner as to define a longitudinal path into the housing, through to aplanar waveguide chemical sensor 25 and out of the housing 27 (notshown). The end face of the housing 27 has dowel holes (one of four isdesignated with numeral 23) to enable the reliable and accurate locationof additional plates upon which may be mounted electromagnetic radiationsources (such as a laser diode for example), electromagnetic radiationdetectors (such as a photodiode array for example) and other optionalcomponents such as lenses. The housing has a circular aperture 24 whichallows the electromagnetic radiation to pass therethrough (to the planarwaveguide chemical sensor 25). The aperture 24 also has a recess 26which enables a window capable of transmitting the electromagneticradiation to be fitted. This ensures that the sensor 25 is sealed fromthe surroundings in terms of potential chemical interference. A meansfor transporting the analyte to the sensor has been omitted from thisFigure for the sake of clarity but is described in detail hereinafter.

An exploded cross-section of the optical assembly of an embodiment ofthe device of the invention is provided in FIG. 3. Shown removed fromthe housing 30 are the sensor holder 32 and sensor 35 with longitudinalcavities 34 a and 34 b allowing the majority of the leading and trailingedges of the sensor to be exposed in free space. The sensor 35 isinserted into the housing 30 such that the top surface of the sensor 35makes contact and seals (in a gas/liquid type manner) with the sensorhousing seat 36. The apertures 37 for the passage of electromagneticradiation and the recesses for the windows 38 allow the transmission ofelectromagnetic radiation. The windows themselves have been omitted forthe sake of clarity. The dowel holes 33 are shown occupied by dowels 39.The channel 40 for the passage of analyte over the surface and theconduits 41 for the transmission of the analyte to and from the sensorsurface are shown. In this embodiment, the conduits 41 are terminatedwith ¼″28 UNF inverted cone fittings (made by OMNIFIT) 42 to provide amechanical connection to the desired test source.

FIG. 4 shows in detailed cross-section the optical assembly of anembodiment of the invention. The holder 32 and sensor 35 are shownseparately in FIG. 4i. The housing is shown separately in FIG. 4iii withwindows 43 and a plate mounted with a laser diode 44 and a plate mountedwith a photodetector array 45. The precise location of the plates isachieved by the dowels 39. The housing seat 36, the channel for testmaterials 40 and the conduits 41 are as hereinbefore described. FIG. 4iishows the complete assembly with the holder 32 and sensor 35 in place inthe housing 30. The positioning of holder 32-in housing 30 creates adead volume 40. The volume around the ends of the sensor 46 is minimisedto reduce effects due to external or ambient chemical changes. FIG. 4iiishows the inverted cone fittings for connection to the device of theinvention and transmission of analyte.

FIGS. 5i and 5 ii show a partial cross-section and plan viewrespectively of the sensor housing seat which seals to the surface ofthe sensor 35. The seat or seal 36 provides a complete gas tight seal tothe surface of the sensor 35. The conduits 41 allow the passage of testanalyte to and from the sensor surface via the channel 40 which allowsthe analyte to come into intimate contact with the sensor surface.

FIG. 6 illustrates an assembled holder 61 and housing 62 of an opticalassembly of a device of the invention. The sensor 68 compriseswaveguides 63 and 64 together with a spacer 65 which may be depositedwhen the sensor is manufactured. Provided the spacer thickness andheight of surface A are known relative to the position ofelectromagnetic radiation source 66, the electromagnetic radiation willfall substantially wholly on the waveguides. The holder and housing aremade opaque to the wavelength of electromagnetic radiation to reducestray output to the detector 67. Engineering tolerances are around 200μm.

FIG. 9 illustrates an assembled holder 61 and housing 62 similar to FIG.6 but with the spacer 65 a provided on the seats 65 b. This improves theexposure of the sensing layer to test material.

In the embodiment of FIG. 7, the sensor 71 is provided with referenceand sensing waveguides (72 and 73), spacer 74 and a silicon baseplate75. Optical fibre 76 is located in a V-groove 77 of baseplate 75. Theposition and height of the emitted light relative to the siliconbaseplate is determined by the V-groove. The baseplate has hole 78etched in it over which the sensor is located. The height of thewaveguide relative to light from the fibre is set by the spacer whichadditionally seals the hole 78 by being sufficiently flat. Stray lightis emitted into the silicon. A discrete detector may be used to monitoroutput or an imaging fibre or fibre array may be used to collect outputimages, or a detector system may be incorporated (integrated) in thebaseplate.

In the embodiment of FIG. 8, the sensor 81 of the optical assembly isprovided with reference and sensing waveguides 82 and 83, a spacer 84and a silicon baseplate 85. Laser 86 is integrally located in thesilicon baseplate. Thus, this embodiment represents an integratedelectro-optic device in which the laser source 86 is integrated in thesilicon baseplate. Output may be discrete, integrated or fibre optic asdescribed hereinbefore.

FIGS. 10 to 18 are intended to illustrate in detail the variouscomponents and stages of construction of a preferred embodiment of adevice of the invention. The materials of the various components havebeen tailored to provide optimum thermal performance and will bedescribed hereinafter and (in particular) with reference to the key toFIG. 18.

FIG. 10 illustrates an optical assembly of a preferred embodiment of theinvention. This is similar to those optical assemblies illustrated inFIGS. 1 to 9 except that the holder and housing are integral to the mainbody of the optical assembly (10 m) rather than being separable parts.

Outer part (10 b) comprises a mounting plate (10 d) made of a suitableengineering material with good insulating properties which has locatingholes (10 e) for long reach countersink bolts (10 a) and a photodiodearray (10 c). A spacer/window retainer (10 f) made of the sameengineering material comprises locating holes (10 g and 10 i) for thebolts (10 a) and a broad aperture (10 h) to allow output light from thesensor to reach the photodiode (10 c). A recess (10 j) retains a window(10 k) in the correct position during assembly. The window (10 k) ismade of 4 mm thick quartz and is sealed to the main body by an o-ring(101) which may be constructed of Viton or a higher performanceelastomer which is held in a seat (10 n and 10 q) on the exit face ofthe main body (10 m) of the optical assembly.

The main body (10 m) is made of a high performance insulating materialwhich has good mechanical strength and is readily machineable. Anexample of such a material is Duratec 750. Locating holes (10 x and 10s) are provided for the long reach bolts (10 a) and the sensor is heldin position by two stainless steel part cylinders (10 p and 10 v). Theupper part cylinder (10 v) is threaded to accept the inlet and outletpipework (not shown) which pass through the main body at inlet/outletconduits (10 j′). Access to the surface of the sensor (10 u) is possibleby virtue of the void created between the upper part cylinder (10 v) andthe sensor (10 u) by an intervening gasket (10 o). This is made of ahigh performance (in terms of chemical resistance and low absorbance)polymer such as Viton. The sensor is mounted on a part cylindricalsensor base (10 p) which is made of stainless steel. A cavity (10 r)exposes the rear face of the sensor base (10 p) to enable subsequentconstruction of the inner Peltier assembly (described hereinafter). Theentry face of the main body (10 m) contains an o-ring seat (10 t and 10w) on which an o-ring (10 y) mounts to provide a seal with an inputwindow (10 z) in the form of a 4 mm quartz construction.

Long reach countersink bolts (10 a) inserted in the locating holes 10 d,10 e, 10 g, 10 i, 10 x and 10 s and into the copper shroud (not shown)assist in holding the optical assembly together. They may be made ofsteel for high-pressure applications or of nylon (which is advantageousfrom the thermal management perspective) where demanding pressurespecifications are not required.

FIG. 11 shows the components of the inner Peltier assembly of apreferred embodiment of the invention. This comprises an inner Peltiermount (11 e) which is made of a good conducting material (eg copper—ifit is electrochemically compatible with stainless steel with regard tocorrosion) which may be fixed (11 a) to the sensor base (11 f) which isin intimate thermal contact with the sensor (11 g). The inner Peltiermount (11 e) is adapted to receive a locating countersink bolt (11 a)which enables it to be bolted to the sensor base (11 f and see reference10 p in FIG. 10). The inner Peltier mount (11 e) has a concave undersidein order to make optimum thermal contact with the sensor base and achannel (11 b) to provide a mounting point for a 2 mm thermistor. Aninner Peltier (11 c) is mounted directly on the inner Peltier mount (11e) and is insulated by a surround (11 d). The surround (11 d) may bemade of a foam type material or mechanically sound insulating materialas desired. Parts (11 d), (11 c) and (11 e) may be bonded with anappropriate thermally conducting adhesive if desired.

The inner Peltier assembly is also shown in plan view in FIG. 11 withthe Peltier lead out (11 h). It is important to insulate the thermistorfrom the inner Peltier (11 c) and to separate the thermistor and Peltierwires whilst they are in close proximity to the inner Peltier itself.

The sensor (11 g) and sensor base (11 f) are located in the main body ofthe optical assembly which is bolted into a copper heat shroud(described hereinafter). The inner Peltier assembly is generallyconstructed within the cavity of the optical assembly which exposes thesensor base. A jig may be required to construct parts (11 e), (11 c) and(11 d) and to route the inner Peltier and thermistor wiring prior toplacement in the cavity of the optical assembly.

FIG. 12 illustrates a circular embodiment corresponding to the squareembodiment shown in FIG. 11. This is a simpler machining proposition andit will be appreciated that where square apertures are depicted in otherFigures, circular may be equally appropriate.

FIG. 13 illustrates schematically a cross sectional side elevation of anoptical assembly and inner Peltier assembly. Peltier wiring (13 b) and athermistor (13 a) are shown. In addition, a part of the Peltier exhaustassembly (13 c) and the attendant insulation (13 d) are shown. These aredescribed in greater detail hereinafter.

FIG. 14A illustrates a heat shroud (14Ae) and integral laser moduleholder (14Ac). During the initial construction stage, slot (14Aa) allowsthe optical assembly to slide into the heat shroud without interferingwith the inlet and outlet pipes. If the pipes are easily removable, theslot may be replaced with one or more appropriately positioned accessholes. An opening (14Ab) and associated slot allow access to the cavityof the optical assembly (see FIG. 10 reference r) into which the innerPeltier assembly is placed in a subsequent construction stage.

The laser module is mounted (in the next stage of construction) in thelaser module holder (14Ac) at one end of the heat shroud (14Ae). Theouter diameter of the laser module holder (14Ac) is designed to be equalto that of the inner diameter of the main body of the optical assembly(FIG. 10 reference m). Thus the machining of the high performanceinsulator can be used to insulate the laser module holder too. The endelevation shows details of the slot and the six tapped holes (14Ad) inwhich the long reach countersunk bolts (FIG. 10 reference a) are locatedto hold the optical assembly together.

FIG. 14B illustrates an exploded view of the optical assembly with thelaser module holder, laser module and heat shroud. The optical assemblycomprises a photodiode and mount (14Bb), spacer/window retainer (14Bc),window (14Be), o-ring (omitted for clarity), main body (14Bf) (detailomitted for clarity), o-ring (omitted for clarity) and window (14Bg)which locates in recess (14Bm). A conducting plate (14Ba) retains thecomponents of the optical assembly in place within the copper heatshroud (14Bh) with the assistance of long reach countersink bolts whichhave been omitted for clarity.

The laser module (14Bj) may be secured with two Allen bolts and is closefitting into the laser module holder (14Bp). An insulating collar (14Bi)is placed over the laser module holder (14Bp). The ribbon cable outputof the photodiode array (14Bk) and the two-core output of the lasermodule (14Bl) are also shown for the sake of completeness.

FIG. 14C illustrates the constructed optical assembly and heat shroud inboth side and end elevation. Internal detail has been largely omittedfor clarity. A section of the main body of the optical assembly(reference Bf in FIG. 14B) is clearly visible (14Ca), as is the majorityof the sensor base (FIG. 10 reference p) which is exposed by opening(14Cb).

The next stage of construction involves fitting the Peltier exhaustassembly as illustrated in FIGS. 15A-C. Thus Peltier exhaust guide(15Aa) in the form of a ring made of an insulating engineering materialfits over the insulating collar of the laser module (15Ab) and compriseslocating lugs (15Ac) which fit into the exhaust slot (15Ad). Asillustrated in FIG. 15B, an insulating plate (15Ba) is fitted into theconstruction (15Bb) to isolate the laser module and its lead outs (15Bc)and the heat shroud from the Peltier exhaust assembly.

At this stage, the inner Peltier assembly is located in the cavity ofthe optical assembly in thermal contact with the sensor base. Thus theinner Peltier mount, inner Peltier, insulating surround (FIGS. 11 and 12references c, d and e) and a conducting block (15Bd) it required tobring the assembly up to the appropriate level to be inserted into thecavity of the optical assembly (15Be) as described hereinbefore.

An exhaust strip (15Cd) of copper or an equivalent material is laid in aslot created by the exhaust guide (15Cf) and a mechanically rigidinsulator (15Ce) (made of Duratec 750 or an equivalent material). Theexhaust strip makes good thermal contact with the inner Peltier assemblybeneath it (not shown for clarity) and the exhaust plate (15Ca) which isinserted in the end of the construction. The laser module lead-outs(15Cc) are brought-around the exhaust strip (15Cd).

In FIG. 16, a restraining sleeve is shown in side and end elevation. Theprimary purpose of the restraining sleeve is to restrain and force thePeltier exhaust assembly on to the inner Peltier assembly at one end andthe exhaust plate at the other. At the same time, it may usefullyprovide cable conduits for the laser module, inner Peltier assembly andthe thermistor. In principle, the outer casing (see FIG. 18) couldperform the function of the restraining sleeve. However the ease ofconstruction may be compromised and so a separate sleeve is preferred.

In FIG. 16A, the restraining sleeve is constructed of an insulatingengineering material. The aperture (16Ac) provides exposure of a widearea of the copper shroud for thermal contact to an outer Peltierassembly. The slot (16Ab) allows the sleeve to slide over the opticalassembly. As with the copper shroud, this may be replaced by one or moreholes if the input and output pipes are easily detachable from theoptical assembly. Slots (16Ad and 16Ae) provide two cable conduits. Thisallows the potentially hot leads of the inner Peltier to be routedseparately from the thermally passive thermistor and laser modulelead-outs.

In FIG. 16B, the photodiode ribbon cable has been omitted from thedrawings for clarity. The exploded view shows how the restraining sleeveslides over the heat shroud and Peltier exhaust. In this stage, thelaser module and thermistor lead-outs (16Ba and 16Bb) which arethermally passive are fed down a first conduit (16Bf) of the restrainingsleeve, whilst the thermally active lead-outs of the inner Peltier(16Bc) are fed down a second conduit (16Bg). The sleeve runs down thelength of the exhaust strip (16Bd) firmly restraining the strip on theinner Peltier assembly at one end and the exhaust plate at the other.The sleeve cam then be slid over the construction with the lead-outsbeing fed down the appropriate conduits as the sleeve progresses. Theaperture (16Be) expose a significant area of the copper heat shroud toenable the closing stages of construction to proceed.

In FIGS. 17A and 17B, the outer casing is shown in sparing detail inside elevation and cross-section. It is constructed in two parts from aninsulating engineering material. The upper part (17Ae) provides athermal void (heated by the end plate of the optical assembly that is inthermal contact with the copper,shroud) in which the control electronicsreside. The main part of the outer casing (17Af) ‘snap fits’ to theupper half at the joint (17Aa). The shoulder (17Ab) retains the exhaustplate. An aperture (17Ad) is provided to allow full access for an outerPeltier assembly. Two hooks are provided (17Ac) which enable the springclip of the CPU heat sink and fan assembly to be employed to force it onto the rest of the assembly. This has been depicted as using the cliplongitudinally. This tends to put stress on the joint (17Aa) which isundesirable. An alternative strategy is to mount the spring clip hookslaterally with both hooks on either the upper part (17Ae) or the mainpart (17Af) of the outer casing. A means for mounting the outer casingto a base plate or other component may be provided if desired.

The outer Peltier mount of the outer Peltier assembly illustrated inFIG. 17B is similar to (although much larger than) that of the innerPeltier mount. It provides a large area of thermal contact with thecopper heat shroud. A conduit mounts the thermistor (17Ba) and channels(17Bb) provide a means to effect the Peltier lead-out. The restrainingsleeve and outer casing provide the coarse alignment of outer Peltierand outer Peltier mount. The fully assembled device is illustrated inFIG. 18 in two side elevation views (at 90° to each other). In theleftmost illustration, the void for the electronics is clearly visible(18 a) which is provided by the upper part of the outer casing (18 c).The main body of the outer casing (18 d) provides a mount for a coolingfan (18 b) for the inner Peltier exhaust plate. However it may bepossible (and expedient) to include a second pair of hooks to enable theuse of a second CPU heat sink/cooling fan spring clip system.

In the rightmost illustration, the lead outs from the outer Peltier andthermistor pairing (18 e and 18 f) and the photodiode ribbon cable (18k) are shown. The lead-outs from the laser module and the inner Peltierassembly have been omitted for clarity. The outer Peltier mount (18 h)can be seen with the thermistor in place upon which is positioned theouter Peltier (18 g). The CPU heat sink (18 j) and fan assembly (18 b)are retained on the Peltier (18 g) by the spring clip (18 i). Insulatingfoam (18 l) has been placed around the perimeter of the outer Peltier(18 g) where it is exposed to the external environment.

The key appropriate to FIG. 18 is as follows:

What is claimed is:
 1. A device for housing a planar optical componentfor use in sensing, said device comprising: an optical assembly adaptedto mount the planar optical component so as to define a longitudinalpath through the device in which the planar optical component iseffectively exposed in free space and including guiding means forcorrelating along said longitudinal path the position of said planaroptical component and of a source of electromagnetic radiation, wherebyto expose said planar optical component to said electromagneticradiation along said longitudinal path whilst substantially eliminatingstray electromagnetic radiation, wherein the optical assembly comprisesa cavity which permits access to a face of the planar optical componentor to a face of a base with which the planar optical component is inintimate thermal contact whereby to enable an inner temperaturecontroller to be positioned in thermal contact with the planar opticalcomponent for controlling the temperature of the planar opticalcomponent, wherein the inner temperature controller is an inner Peltierassembly capable of adding heat to or dissipating heat from the planaroptical component, said inner Peltier assembly comprising an innerPeltier mounted on an inner Peltier mount, and a Peltier exhaustassembly which permits thermal transfer from an exhaust side of theinner Peltier to the environment.
 2. A device as claimed in claim 1wherein the Peltier mount has a concave underside to optimise thermalcontact with the planar optical component or with a base with which theplanar optical component is in intimate thermal contact.
 3. A device asclaimed in claim 1 wherein the planar optical component is a sensor. 4.A device as claimed in claim 3 wherein the sensor is mounted on a sensorbase and is in intimate thermal contact therewith.
 5. A device asclaimed in claim 1 wherein the optical assembly and inner temperaturecontroller are contained within a conducting sleeve.
 6. A device asclaimed in claim 5 wherein the conducting sleeve comprises a copper heatshroud.
 7. A device as claimed in claim 6 wherein the copper heat shroudis provided with an opening which is suitably disposed to coincide withthe cavity in the optical assembly thereby allowing the inner Peltierassembly to be inserted in the optical assembly after the opticalassembly has been inserted in the conducting sleeve.
 8. A device asclaimed in claim 6 wherein the heat shroud comprises an integral lasermodule holder for inserting a laser module.
 9. A device as claimed inclaim 1 wherein the Peltier exhaust assembly comprises: an exhaust platepositioned to allow thermal exchange with the environment.
 10. A deviceas claimed in claim 1 wherein the Peltier exhaust assembly comprises:means for thermally contacting the inner Peltier assembly with theexhaust plate.
 11. A device as claimed in claim 10 wherein the means forthermally contacting the inner Peltier assembly with the exhaust plateis a thermally conducting exhaust strip.
 12. A device as claimed inclaim 1 wherein the Peltier exhaust assembly comprises: an exhaust guidecapable of fitting over the insulating collar of a laser module.
 13. Adevice as claimed in claim 12 wherein the exhaust guide defines a slotinto which the thermally conducting exhaust strip may be inserted.
 14. Adevice as claimed in claim 1 further comprising: an outer temperaturecontroller which permits coarse temperature control of one or more ofthe group selected from the conducting sleeve, laser module,laser-module holder, the exterior parts of the optical assembly and theelectronics.
 15. A device as claimed in claim 14 wherein the outertemperature controller takes the form of an outer Peltier assembly. 16.A device as claimed in claim 15 comprising: means for urging the Peltierexhaust assembly onto the inner Peltier assembly.
 17. A device asclaimed in claim 16 wherein the means for urging is a restraining sleeveadded outwardly of the heat shroud to force the Peltier exhaust assemblyonto the inner Peltier assembly at a first end and the exhaust plate atthe other.
 18. A device as claimed in claim 17 wherein the outer Peltierassembly is provided externally of the restraining sleeve, saidrestraining sleeve provided with an aperture to enable exposure of aneffective area of the conducting sleeve to achieve thermal contact withthe outer Peltier assembly.
 19. A device as claimed in claim 1 which iscapable of sequential construction from a plurality of discreteassemblies, said assemblies being: an optical assembly contained withina conducting sleeve; an inner Peltier assembly comprising an innerPeltier; and a Peltier exhaust assembly, wherein: (1) the inner Peltierassembly is housed within the cavity of the optical assembly so as toachieve intimate thermal contact with the planar optical component and(2) the Peltier exhaust assembly permits thermal transfer from theexhaust side of the inner Peltier to the environment and is thermallyisolated from the conducting sleeve.
 20. A device as claimed in claim 19further comprising a discrete outer Peltier assembly in thermal contactwith the conducting sleeve.
 21. A device as claimed in claim 1 whereinthe planar optical component has a plurality of waveguides.
 22. Aprocess for constructing a device for housing a planar optical componentfor use in sensing, said device comprising an optical assembly adaptedto mount the planar optical component so as to define a longitudinalpath through the device in which the planar optical component iseffectively exposed in free space and including guiding means forcorrelating along said longitudinal path the position of said planaroptical component and of a source of electromagnetic radiation, wherebyto expose said planar optical component to said electromagneticradiation along said longitudinal path whilst substantially eliminatingstray electromagnetic radiation, wherein the optical assembly comprisesa cavity which permits access to a face of the planar optical componentor to a face of a base with which the planar optical component is inintimate thermal contact whereby to enable an inner temperaturecontroller to be positioned in thermal contact with the planar opticalcomponent for controlling the temperature of the planar opticalcomponent, the process comprising the steps of: inserting an opticalassembly in a conducting sleeve comprising an integral laser modulehousing; inserting a laser module into the laser module housing; housingan inner Peltier assembly in the cavity of the optical assembly so as toachieve thermal contact with the planar optical component; andpositioning a Peltier exhaust assembly in thermal isolation from theconducting sleeve so as to permit thermal transfer from the exhaust sideof the inner Peltier to the environment.
 23. A process as claimed inclaim 22 comprising the additional steps of: constructing an outerrestraining sleeve; constructing an outer casing; and positioning anouter Peltier assembly on the outer casing or restraining sleeve wherebyto achieve thermal contact with the conducting sleeve.
 24. A device forhousing a planar optical component for use in sensing, said devicecomprising: an optical assembly adapted to mount the planar opticalcomponent so as to define a longitudinal path through the device inwhich the planar optical component is effectively exposed in free spaceand including guiding means for correlating along said longitudinal paththe position of said planar optical component and of a source ofelectromagnetic radiation, whereby to expose said planar opticalcomponent to said electromagnetic radiation along said longitudinal pathwhilst substantially eliminating stray electromagnetic radiation,wherein the optical assembly comprises a cavity which permits access toa face of the planar optical component or to a face of a base with whichthe planar optical component is in intimate thermal contact whereby toenable an inner temperature controller to be positioned in thermalcontact with the planar optical component for controlling thetemperature of the planar optical component, wherein the opticalassembly and inner temperature controller are contained within aconducting sleeve comprising a copper heat shroud, and wherein thecopper heat shroud is provided with an opening which is suitablydisposed to coincide with the cavity in the optical assembly therebyallowing the inner temperature controller to be inserted in the opticalassembly after the optical assembly has been inserted in the conductingsleeve.
 25. A device as claimed in claim 7 wherein the inner temperaturecontroller is an inner Peltier assembly capable of adding heat to ordissipating heat from the planar optical component.
 26. A device asclaimed in claim 25 wherein the inner Peltier assembly comprises: aninner Peltier mounted on an inner Peltier mount.
 27. A device as claimedin claim 26, wherein the Peltier mount has a concave underside tooptimise thermal contact with the planar optical component or with abase with which the planar optical component is in intimate thermalcontact.
 28. A device as claimed in claim 24, wherein the heat shroudcomprises an integral laser module holder for inserting a laser module.29. A device as claimed in claim 26, further comprising a Peltierexhaust assembly which permits thermal transfer from an exhaust side ofthe inner Peltier to the environment.
 30. A device as claimed in claim29, wherein the Peltier exhaust assembly comprises: an exhaust platepositioned to allow thermal exchange with the environment.
 31. A deviceas claimed in claim 29, wherein the Peltier exhaust assembly comprises:means for thermally contacting the inner Peltier assembly with theexhaust plate.
 32. A device as claimed in claim 31, wherein the meansfor thermally contacting the inner Peltier assembly with the exhaustplate is a thermally conducting exhaust strip.
 33. A device as claimedin claim 29, wherein the Peltier exhaust assembly comprises: an exhaustguide capable of fitting over the insulating collar of a laser module.34. A device as claimed in claim 33, wherein the exhaust guide defines aslot into which the thermally conducting exhaust strip may be inserted.35. A device for housing a planar optical component for use in sensing,said device comprising: an optical assembly adapted to mount the planaroptical component so as to define a longitudinal path through the devicein which the planar optical component is effectively exposed in freespace and including guiding means for correlating along saidlongitudinal path the position of said planar optical component and of asource of electromagnetic radiation, whereby to expose said planaroptical component to said electromagnetic radiation along saidlongitudinal path whilst substantially eliminating stray electromagneticradiation, wherein the optical assembly comprises a cavity which permitsaccess to a face of the planar optical component or to a face of a basewith which the planar optical component is in intimate thermal contactwhereby to enable an inner temperature controller to be positioned inthermal contact with the planar optical component for controlling thetemperature of the planar optical component; an outer temperaturecontroller which permits coarse temperature control of one or more ofthe group selected from the conducting sleeve, laser module,laser-module holder, the exterior parts of the optical assembly and theelectronics, wherein the outer temperature controller takes the form ofan outer Peltier assembly; and means for urging the Peltier exhaustassembly onto the inner Peltier assembly wherein the means for urging isa restraining sleeve added outwardly of the heat shroud to force thePeltier exhaust assembly onto the inner Peltier assembly at a first endand the exhaust plate at the other.
 36. A device as claimed in claim 35,wherein the outer Peltier assembly is provided externally of therestraining sleeve, said restraining sleeve provided with an aperture toenable exposure of an effective area of the conducting sleeve to achievethermal contact with the outer Peltier assembly.
 37. A device forhousing a planar optical component for use in sensing, said devicecomprising: an optical assembly adapted to mount the planar opticalcomponent so as to define a longitudinal path through the device inwhich the planar optical component is effectively exposed in free spaceand including guiding means for correlating along said longitudinal paththe position of said planar optical component and of a source ofelectromagnetic radiation, whereby to expose said planar opticalcomponent to said electromagnetic radiation along said longitudinal pathwhilst substantially eliminating stray electromagnetic radiation,wherein the optical assembly comprises a cavity which permits access toa face of the planar optical component or to a face of a base with whichthe planar optical component is in intimate thermal contact whereby toenable an inner temperature controller to be positioned in thermalcontact with the planar optical component for controlling thetemperature of the planar optical component, wherein said device iscapable of sequential construction from a plurality of discreteassemblies, said assemblies being: an optical assembly contained withina conducting sleeve; an inner Peltier assembly comprising an innerPeltier; and a Peltier exhaust assembly, wherein: (1) the inner Peltierassembly is housed within the cavity of the optical assembly so as toachieve intimate thermal contact with the planar optical component and(2) the Peltier exhaust assembly permits thermal transfer from theexhaust side of the inner Peltier to the environment and is thermallyisolated from the conducting sleeve.